Yellow fever in São Paulo State prompts vaccination campaign

Two confirmed yellow fever cases in São Paulo State, Brazil (an area considered not at risk for yellow fever transmission) has prompted national authorities to begin vaccination campaigns and strengthening health care services and carrying out risk communication activities.

Public domain image/Deyvid Aleksandr Raffo Setti

Between July and mid-October 2017, a total of 71 suspected yellow fever cases were reported in São Paulo State, Brazil. Of these, two were confirmed, six are under investigation, and 63 were ruled out. The two confirmed cases (one of which was fatal) were reported from Itatiba from 17 September through 7 October 2017.

In addition, from July to early November, 580 epizootics in non-human primates (NHPs) were reported in São Paulo State, with an increase in the number of cases reported from 10 September 2017. Of these, 120 were confirmed for yellow fever, 233 are under investigation, 74 were classified as undetermined, and 153 were ruled out.

These are the first human cases of yellow fever that have been reported in Brazil since June 2017. These cases, alongside the occurrence of epizootics in the urban area of São Paulo City and in municipalities that were previously considered not at risk for yellow fever, are a public health concern, according to the World Health Organization.

Although Brazilian health authorities have swiftly implemented a series of public health measures in response to this event, including mass vaccination campaigns, it may take some time to reach optimal coverage in these areas given the large number of susceptible individuals.

Currently, the number of unvaccinated people in São Paulo City remains high at around 10 million. If yellow fever transmission continues to spread to areas that were previously considered not at risk for yellow fever, ensuring the availability of vaccine and implementing control measures would pose significant challenges.